The present invention relates to a method for controlling a hybrid vehicle, and more particularly to a method for optimally controlling a hybrid vehicle having an engine and a regenerative system which converts, stores and discharges the kinetic energy of the vehicle.
In braking with a drum brake or a disk brake, the kinetic energy of the vehicle is discarded as heat. On the other hand, there are some vehicles which improve fuel efficiency with a regenerative system for making use of their kinetic energy when storing. For instance, a vehicle disclosed in the Japanese Published Unexamined Patent Application No. Hei 10-98805 is equipped with a system which converts kinetic energy into electric energy with a rotary machine and stores the converted energy in its battery. Other known examples include a regenerative system using elastic elements, compressed air, a flywheel, a hydraulic pump and so forth, described in the Basics and Theory, Automotive Technology Handbook, Vol. 1, issued by the Automotive Technology-Society (of Japan), Dec. 1, 1990, pp. 137-140.
A hybrid vehicle equipped with one or another of these regenerative systems can enhance fuel efficiency and driving ease by controlling the output ratio between a primary power source, such as an engine, and a secondary power source consisting of a regenerative system. For instance, a method by which the destination is entered to determine the traveling route and a schedule for the state of charge of the battery on the route, as disclosed in the Japanese Published Patent Application No. Hei 8-126116, can be applied to a vehicle provided with a rotary machine (motor) and a storage battery. According to this method, the state of charge of the battery is increased before an upward slope to help prevent deterioration of the driving conditions due to a power shortage on the climb. Further, by reducing the state of charge of the battery and increasing the quantity of energy regenerated by a regenerative brake, improve fuel efficiency and enhanced driving ease are provided, while ensuring a sufficient level of braking force.
There is a problem in that no long term scheduling can be done unless the destination and the route thereto are indicated. Furthermore, even though the destination and the route thereto are specified and the driving plan is made, if the vehicle deviates from the planned route as a result of an error in driving or a change in the driver""s plans, both fuel efficiency and driving ease will deteriorate.
According to the present invention, a hybrid vehicle is controlled by calculating the distribution of heights the vehicle is predicted to reach for each point of time; calculating the representative value of height at each point of time from this distribution of heights for each point of time; and, it being assumed that the vehicle will pass the point of representative height of that representative value, scheduling the energy recovery and discharge quantities of the regenerative system and the engine output. The method according to the invention makes it possible to make a medium to long range driving plan even where the destination and the route thereto are not specified, and thereby to improve fuel efficiency.
According to the invention, a hybrid vehicle is controlled by calculating the distribution of probabilities pertaining to the energy state of a vehicle at each point of time from the current moment onward, determining the setting range of target energy storage quantity at each point of time according to the dispersion of the distribution of the energy state, and scheduling the energy regeneration and discharge quantities of the regenerative system and the engine output so as to be consistent with the limit range. As a result, when a driving plan is made according to the scheduling method described above, the driving conditions can be enhanced by providing an excess or a shortage of regenerative system energy.
In the method of above, preferably either the distribution of heights or a distribution pertaining to the vehicle speed or both are used as the distribution(s) of probabilities pertaining to the vehicle energy state to control the hybrid vehicle. As a result, a driving plan can be made on the basis of determinants of the state of energy to achieve satisfactory control.
In the method above, a hybrid vehicle is controlled by calculating the reachable point at each point of time and the probability of arriving there from the ratio of branching into different routes at each junction ahead of the vehicle and the predicted time to cover a given section, determining the height of the point to be reached, calculating the distribution of the probabilities of the vehicle""s arrival at a given height at that point of time, and calculating the distribution of probabilities pertaining to the energy state of the vehicle at each point of time on the basis of the distribution of height probabilities so calculated.
A hybrid vehicle is controlled by calculating the distribution of heights of points contained in a set consisting of at least either the points within a prescribed spatial range from the current position of the vehicle or the points reachable within a prescribed length of time, and setting the target quantity of energy storage of the regenerative system so that it become closer to the center of the proper range as the dispersion of the height distribution increases. As a result, the vehicle can be controlled in a relatively small number of procedural steps though inferior in accuracy.